Tuberculosis (TB) disease, which results from infection with Mycobacterium tuberculosis (Mtb), is a leading cause of infectious morbidity and mortality in children < 5 years old worldwide. In TB endemic regions, in which the vast majority of the world's annual 9 million adult cases of TB disease reside, children < 5 years old account for 30-40% of the total patients and those children who are infected tend to have more severe, often fatal forms of TB. A significant contributor to the deadliness of TB in children < 5 years ol is the poor performance of standard TB diagnostics in this age group, especially as compared to adults. Poor diagnostics result in delayed and missed diagnoses, which in turn lead to increased morbidity and mortality in children. Currently, what is needed is a simple, robust immunodiagnostic blood test that will differentiate childhood TB pneumonia from pneumonia not due to TB. We hypothesize that the detection of CD8+ T cells directed toward Mtb peptides can be utilized to distinguish young children with TB pneumonia from those with pneumonia not due to TB. In this regard, CD8+ T cells preferentially recognize heavily Mtb-infected cells and as OHSU investigators, we have observed in Ugandan children < 5 years old, that Mtb-reactive CD8+ T cells are detected in children with TB and not detected in asymptomatic children with Mtb infection/exposure. Taken together, these data suggest that CD8+ T cells correlate with bacterial burden. In parallel, we have defined 45 immunodominant, clinically-validated CD8 TB antigens through our large scale antigen discovery program that are exclusively licensed to ViTi, Inc. from OHSU. To develop an improved diagnostic for children, in our Phase I study, we used a bioinformatic approach to define regions enriched for high affinity binding to HLA within these 45 immunodominant CD8 antigens. We selected 166 peptides representing these regions likely to contain clusters of immunogenic epitopes, and using IFN-? ELISPOT assay, tested the recognition of these peptides by CD8+ T cells isolated from individuals with and without latent TB infection (LTBI). From these data, we selected sets of peptides comprising two peptide pools; one optimized for sensitivity and one for specificity for Mtb infection to be used in prototype immunodiagnostic blood tests, which we will subsequently refer to as ViTi ONESENS and ViTi ONESPEC, respectively. In this Phase II proposal of diagnostic accuracy, we will first determine the sensitivity and specificity of these prototype immunodiagnostic blood tests, in cohorts of Ugandan children < 5 years old hospitalized with pneumonia. Then to further improve upon on these prototype tests, we will apply the same strategy we used in the Phase 1 study to additional novel immunodominant CD8 antigens licensed by OHSU to ViTi Inc. to create improved peptide pools to be used in ViTi TWOSENS and ViTi TWOSPEC. Finally, we will determine the sensitivity and specificity of ViTi TWOSENS and ViTi TWOSPEC in the same cohorts of Ugandan children < 5 years old hospitalized with pneumonia.